replace some control characters with their symbol counterparts

src/ui/bigtext/line.py

@@ -36,12 +36,34 @@ class Line:
         prefix_chars = prefix_bytes.decode("utf8", errors="ignore")
         return len(prefix_chars)
 
-    def line_tabs_replaced(self):
+    def line_prepared_for_display(self):
+        line = self._line_tabs_replaced()
+        line = self._replace_control_chars_with_pictures(line)
+        return line
+
+    def _replace_control_chars_with_pictures(self, line: str):
+        length = len(line)
+        for i in range(length):
+            c = line[i]
+
+            if unicodedata.category(c) == "Cc" and c != "\r" and c != "\n" and c != "\t":
+                ordinal_value = ord(c)
+                if ordinal_value < 32 and not ordinal_value in [9, 10, 11]:
+                    # print(ord(c), " -> ", hex(ord(c)), " -> ", unicodedata.category(c), " -> ", chr(9216 + ord(c)))
+                    line = line.replace(c, chr(9216 + ord(c)))  # see Unicode Block “Control Pictures”
+                else:
+                    # print(ord(c), " -> ", hex(ord(c)), " -> ", unicodedata.category(c), " -> \u2421")
+                    line = line.replace(c, "\u2421")  # symbol for delete (␡)
+                # print(line)
+
+        return line;
+
+    def _line_tabs_replaced(self):
         line = self._line;
         i = 0
         offset = 0
         result = ""
-        length = len(line)
+        # length = len(line)
         while True:
             tab_index = line.find("\t", offset)
             if tab_index < 0: